chemical dominoes
section 1
Energy and Entropy: Alternative
Reaction Pathways
Section Overview
In this section, students are exposed to the idea
of state functions by exploring different ways to
get an object from a starting location to an ending
location. They practice establishing criteria to
select the best approach and evaluate approaches
using those criteria. Then, students compare
different ways of producing carbon dioxide gas.
They brainstorm criteria for selecting which
method might be best for using in the chemical
dominoes apparatus. After an introduction to
two chemical concepts (endothermic/exothermic
changes, entropy increase/decrease) and drawings
of arrangements of particles in different states
(before/after), each student in the group
becomes an expert in the chemistry changes that
occur in one of the carbon dioxide production
methods. Students then return to their groups
and determine the best method considering both
chemistry criteria and their initial group’s criteria.
Background Information
Closed Systems
To be able to talk about what happens during a
change, we must define exactly what is changing.
A closed system is a set of interrelated parts that
do not exchange any matter or energy (in or
out) with the surroundings. However, in reality,
some energy can usually flow between a system
and its surroundings. A closed pot of hot coffee
is an example of a closed system. As long as the
cover remains securely closed, no matter (not
even steam) escapes or enters the pot. However,
over time the coffee inside will cool, as a result
of losing heat energy to the surrounding air and
the counter on which the pot sits. Defining what
is changing, then, involves drawing an imaginary
614
surface around the system. If an imaginary surface
can be drawn in such a way that no matter can
enter or leave the system, but heat can flow
between the system and its surroundings, then
what is inside the surface is a closed system. In
chemistry, we are usually concerned with changes
that take place in some chemicals. If the chemicals
are in a container, then it is possible to imagine
a surface around the entire container, so that the
contents of the container form the system.
State Functions
The concept of alternative pathways is a
principal feature in describing state functions
in thermodynamics. A state function is a
measurement or number that describes the state
of a system. When changing from one state to a
second state, the difference between the first and
second states does not depend on the path taken
to get there. For example, altitude change (vertical
displacement) is a state function if you are talking
about traveling from one location to another. If
you travel from Boston, Massachusetts (elevation
25 ft) to Boulder, Colorado (elevation 5300 ft),
the altitude change is 5275 ft. It doesn’t matter if
you fly directly there, drive there, travel around
the world for a year first, or take a circuitous
path on an airline that routes you through three
layovers in Dallas, San Francisco and Chicago
before you get there. In the end, your altitude
change is still 5275 ft. Another example illustrates
the importance of state functions in systems in
chemistry. For a fixed quantity of gas in a closed
system, the pressure, volume and temperature
describe the state of the gas. A system can change
from one state to another state by many different
paths. For example, if changing a sample of gas
from a state of P = 1 atm, V = 2 L, and
T = 300 K to a state of P = 4 atm, V = 1 L,
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
Energy and Bond Formation
When matter gains or loses energy, the total
energy of the matter and surroundings is
conserved. This means the energy has to come
from somewhere and to go somewhere. It must be
accounted for. Focusing on the particles of matter
themselves, heat energy can go into the system,
thereby increasing the motion of the particles.
Or a decrease in the motion of the particles
is accompanied by a release of heat to the
surroundings. In a gas, particles can move about
faster or slower on average. In a solid, particles
can vibrate faster or slower on average. In this
section, we will focus on bond energy.
Breaking and forming bonds involves energy
changes. A bond forms between two atoms
because forming that bond is advantageous —
that is, a lower energy is achieved. Forming a
bond causes atoms to have lower potential energy
states which are usually preferable in nature.
To be advantageous, the system must move from
a state of higher potential energy to a state of
lower potential energy. A useful analogy is that
it is advantageous for a ball to roll down a hill,
not up. If the energy of a system decreases, then
the system must release the potential energy. If
it is released as heat, then the surroundings will
chapter 4
and T = 600 K, many paths to the final state are
possible. One could first decrease the volume to
1 L while maintaining constant temperature
(the pressure would therefore change), and
after that raise the temperature to 600 K while
maintaining constant volume (the pressure
would finally be 4 atm). Alternatively, one could
simultaneously heat the gas to 600 K while also
compressing the volume to 1 L/mol. Again, at the
end the pressure would be 4 atm. The changes
in pressure, in volume, and in temperature are
always the same, no matter the path. Enthalpy
and entropy are also state functions. For a state
function, the path taken does not affect the
initial and final states. When multiple pathways
can achieve the same change, criteria must be
established to decide which pathways are better
than others.
be warmer. A release of heat energy by a system
is a sign of an exothermic reaction. So, bond
formation is exothermic because the bonded
atoms are at lower potential energy than the
unbonded atoms, and energy must leave the
system in order to conserve energy. Conversely,
breaking a bond is an endothermic change and
the products are at higher potential energy.
Hydrogen atoms are not found isolated in nature
because it is energetically advantageous (lower
energy) for hydrogen atoms to bond to many
other kinds of atoms, including other hydrogen
atoms. The difference between the potential
energy of two unbonded neutral hydrogen atoms,
and the minimum potential energy where the
two atoms are bonded, is the amount of energy
released by the atoms when they form the bond.
This is an exothermic change because the system
loses energy, and that energy must be taken up by
the system’s surroundings
Entropy
Students are also introduced to disorder in this
section. Disorder changes can be most easily
understood by comparing how particles are
arranged in starting materials vs. in ending
materials (that is, by looking at the arrangements
of materials in solid, liquid, and gas states, and
also at whether they are pure or mixtures).
Students are asked to compare the total disorder
of the starting materials to the total disorder of
the ending materials. If the magnitude of entropy
increases, then disorder increases.
Engineering Design
Engineering design is an important component
of technology. Technology is “the process by
which humans modify nature to meet their needs
and wants.”1 One component of technological
literacy is design. Specifically, the International
Technology Education Association (ITEA) has
established three standards relating to design:2
• D
esign is the first step in making a
product or system. Several characteristics
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615
chemical dominoes
define the process: it is purposeful, based
on certain requirements, systematic,
iterative, and creative, and there are
many possible solutions.
• Engineers developing a technology use an
approach called the Engineering Design
Process. This process demands critical
thinking, the application of technical
knowledge, creativity, and concern with
the effects of the technology on society
and the environment.
• Engineering design is but one problemsolving process. Other approaches
include troubleshooting, research and
development, invention and innovation,
and experimentation in problem solving.
Troubleshooting is sure to be used by students
in developing the Chapter Challenge. Effective
troubleshooting is systematic in eliminating
various possible explanations while focusing
on the source of a problem. Students may also
engage in other approaches as they design a
chemical dominoes apparatus.
National Academy of Engineering, National Research Council (2002).
Technically Speaking: Why All Americans Need to Know More About
Technology. (Washington, D.C.: National Academy Press.)
2 ITEA (2000). Standards for Technological Literacy: Content for the
Study of Technology. (Reston, VA: ITEA.)
1
Learning Outcomes
learning outcomes
Apply the Engineering Design
Cycle to scientific and everyday
situations.
Investigate,
Preparing for the
Chapter Challenge
Evidence of Understanding
Students are able to generate CO2 gas using four
different methods.
Generate evaluation criteria and Investigate
use those criteria to compare
Steps 3, 6
and evaluate various methods
to achieving a goal.
Students use data they recorded from the various methods
of CO2 gas production to select one that best achieves the
desired results.
Determine how energy and
disorder change during physical
and chemical processes.
Students’ observations and answers match those given in
this Teacher’s Edition.
Notes
616
Location in Section
Chem Talk,
Chem Essential Questions,
Chem to Go
Questions 1-6
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
chapter 4
Section 1
Materials, Chemicals, Preparation, and Safety
(“per Group” quantity is based on group size of 4 students)
Materials and Equipment
Materials
(and Equipment)
Chemicals
Quantity
per Group
(4 students)
Ringstand
1
Clamp for Erlenmeyer flask
1
Erlenmeyer flask, 125 mL
1
Scoopula
1
Weighing boats
1
Meter stick
1
Hot plate
1
Wire gauze squares
1
Balloons (High quality latex that
will expand with low pressure)
1 (Have
spare balloons
on hand)
Fulcrum (Anything that you have
available should work, such as a
piece of cardboard or wood, with
a pencil taped to it)
1
Graduated cylinder, 10 mL
1
Rubber bands
Materials (and Equipment)
Balances, 0.01 g
1 box
Quantity
per Class
(24 students)
2
Beaker, 1 L
1
for Method 4
Carbonated beverage, 12 oz.
(seltzer is best)
1 bottle
for Method 4
Vinegar, 1 pt
50 mL
for Method 1
Note: Only 1-2 groups will experiment with each method.
The amounts given above are more than enough for multiple
experiments, if desired.
Chemicals
Quantity
per Class
(24 students)
Sodium bicarbonate, NaHCO3,
baking soda
35 g
for Method 1
Calcium carbonate, CaCO3
70 g for
Methods 2-3
Hydrochloric acid, HCl, 1.0 M
150 mL
for Method 2
Teacher Preparation
1.0 M Hydrochloric acid (HCl)—In a fume hood,
slowly and carefully, with stirring, add 83.3 mL
of concentrated hydrochloric acid (12 M) to
about 800 mL of deionized water and then
adjust the volume to 1000 mL. Note that the
fumes coming from concentrated hydrochloric
acid are very irritating. This amount should be
enough for both Section 1 and Section 2.
Safety Requirements
• Goggles
and aprons are required in the
laboratory area.
• Methods
1, 2, and 4 can be flushed down
the sink. Method 3 can go into the trash
when cool.
• Wash
arms and hands before leaving the
laboratory area.
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chemical dominoes
Meeting the Needs of All Students
Differentiated Instruction
Augmentation and Accommodations
Learning issue
Anticipatory set
Reference
What Do
You See?
Accommodations
•D
ifferentiate questions about the art to encourage all students to become
engaged in the task ahead. Start with open-ended opinion questions such
as, “What part of the picture do you like the best?” Some students may not
immediately see the events as a sequence. Begin to explore the concept of
action/reaction by asking a student to read the blackboard in the picture.
Point out the sleeping student. Ask how the other students wake him up.
Save more capable volunteers to extend the class’s understandings.
Frustration tolerance
and persistence
Investigate
1.
Accommodations
• S ome students get frustrated more easily than others. Make sure that group of
students chooses a method of producing carbon dioxide that works well and
produces a significant amount; otherwise, they may give up or become off task.
Recording
observations,
organizing data
Investigate
3.
Augmentation
•A
sk students to create a chart in which to record the time, volume, mass of
the starting materials, qualitative data, etc. Teach them to organize their
observations by making some decisions as a class about which data needs to
be recorded and how it should be organized into a table.
Accommodations
•G
ive students a table already set up for recording observations. Leaving some
information for them to provide will help them develop their own ability to
organize data.
Determining
the amount of
substances to use in
the reaction
Investigate
3.
Accommodations
• F or those who may have difficulty determining the amount of each substance,
tell them how much they should use.
• F or students who may still have difficulty, provide them with pre-measured
portions as done with most TV cooking demonstrations.
Interpretation of
symbols
Investigate
Methods 1-4
Augmentation
•A
n equation of the reaction for each method is included, but the symbols
which describe the physical state are only explained in the Method 1 section.
Go through this with the class before they begin. Then point out the use of
symbols in the other three sections. Check for understanding by asking
students to explain the symbols in the other reactions.
Class participation
Understanding the
concept of action/
reaction
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Augmentation and Accommodations
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
Reading
comprehension
Reference
Understanding
endothermic and
exothermic change
Augmentation and Accommodations
Chem Talk
Augmentation
•A
sk groups to read the first section of Chem Talk and list three things which
happen when energy is added. Particles move faster, bonds are broken, and
attractive forces are overcome.
• Ask students to write a definition of bonds and attractive forces which highlights
their differences and compares their strength. Have each student develop a
definition and then create one good definition that the class can record.
•M
odel definition formatting by creating a table which includes each important
aspect of the definition of these terms. It should include key words (within
molecules, between molecules) which illustrate the differences and compare
the energy needed to overcome them.
Chem Talk
Augmentation
•A
sk students to read the first paragraph and stop. Check for understanding
by asking students to write down the kind of change that was involved in the
method they used. Ask several to share their answers and discuss.
Accommodation
•C
reate a question students may use as a cue to determine if an energy change
is exothermic or endothermic.
•H
ave groups create a mnemonic to remember the difference between
endothermic and exothermic. Compare the mnemonics of each group.
Developing
vocabulary
chapter 4
Learning issue
Strategies for Students with Limited English Language Proficiency
Learning issue
Reference
Augmentation and Accommodations
Background
knowledge
Scenario
Students will benefit from more background knowledge of Rube Goldberg
including some examples of his cartoons to help emphasize the point being
made. Additionally, students may need assistance with the concept of marketing
and an explanation of “consumers.” There should be some discussion of how the
students will structure their presentation. Discussions about the properties of toys
might help as well. Have students discuss the criteria to ensure that there is clarity
of expectations.
Background
knowledge
What Do You
Think Now?
Check to make sure that students know the term, “ingredients” and give
examples of things that are “identical.”
Vocabulary
Investigate
Students may not be aware of the use of the term, “arriving” as a synonym for
making a decision. Also check to see if students understand the phrase, “change
in circumstances.” Check on students’ understanding of the word, “apparatus”
(2). Check students’ understanding of the term, “characteristic” (Method 1).
Check to see if students can decode the various formulas.
Background
knowledge
Vocabulary
Comprehending text
Chem Talk,
Chem Essential
Questions
Check for understanding of words such as “undergoes.” Certain signal words may
not be familiar, such as “however,” and “conversely.” At the beginning of each
section is a title in the form of a question. It may be helpful for students to hear
the question asked aloud and then discuss with a partner or in small groups the
possible answer(s). The phrase in the header of the Chem Talk section, “A Matter
of Perspective” may need some explanation. Students may need some direction
on what they are to do when they “describe” in the How do you know? section.
Supporting details
Research skills
What Do You
Think Now?
Students will be asked to support an answer with an explanation. An example
of an assertion supported by details would be helpful, either through a provided
example, or one created with the entire class. A “sidebar” issue could be used
to create an example. Oral language development could include practice in
pronunciation and syllabication exercises.
Comprehension
Vocabulary
Chem to Go
Students are asked to “describe” as one of their responses. It might be helpful
to provide an example of what a description is in this context. Have students
respond in small groups and share consensus answers.
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chemical dominoes
Section 1
What Do You Think?
Teaching Suggestions
and Sample Answers
What Do You See?
Answers will be varied. The main
point is to engage students, to get
them actively involved, and to
introduce some of the topics they
will encounter in this section.
There are no right or wrong
answers, although you may
ask for explanations for their
responses. One of the concepts
introduced by the illustration is a
balloon increasing in size, which
then tips a lever. This is followed
by a sequence of events, ending
in a desired result. Since many
students will not be familiar with
Rube Goldberg, this provides a
good introduction to his work.
These are open questions that
will have varied answers and
they should lead to a good
discussion. Students may have
varied definitions of “identical,”
depending on the context. Some
may interpret it to mean look and
taste identically while others may
interpret it to mean exactly the
same composition. The purpose
of these questions is to guide
students to realize that both the
materials and method used affect
the outcome of any process.
The chocolate-chip cookies could
still be identical if the ingredients
that differ have the same effect
on the cookies. An example
might include one person using
self-rising flour while another
person uses all-purpose flour
with baking powder and salt.
Depending on how students
have defined “identical,” they
might also suggest one person
using a sugar substitute while
another uses sugar. Other
students may contend that the
difference in calories makes the
cookies different.
Students should recognize that
using the same ingredients does
not guarantee the same cookies.
They should note that different
recipes, ratio of ingredients,
cooking times or temperature
variations would result in
different cookies.
Students’ Prior Conceptions
The most important concepts to establish are the
definition of a “system” and thinking from the
perspective of a system. When a change occurs, that
change can be isolated by an imaginary boundary.
Everything inside the boundary is the system and
everything else outside are the surroundings. Key to
identifying types of changes (chemical vs. physical,
endothermic vs. exothermic; increase vs. decrease in
disorder) is being able to reason from the perspective
of the system or the surroundings.
Specific misconceptions that are pervasive include:
1. If a reaction mixture gets hot, it must be
endothermic.3
Students often reason that if a mixture is hot, it
must have absorbed heat from an outside source,
and therefore, must be an endothermic reaction.
The confusion here arises from not taking the
correct perspective. The correct reasoning is that if
the chemicals are hot, it is because they are giving
off heat in the process of the change occurring.
Since the system is the chemicals, then it is the
system that is losing heat energy by giving off heat.
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What Do You Think?
a chemist’s response
Therefore, the change is exothermic.
There are also many misconceptions surrounding
science, engineering, and technology.4 In particular:
2. Intuition and trial-and-error are how scientists
and engineers invent new designs.
These are important aspects of technological
innovation. However, for over 100 years now, we
have used quantitative rules to help guide design.
3. Technology means using computers.
The meaning of the word “technology” has evolved
over time. In the 19th century, technology referred to
practical arts used to create physical products ranging
from wagon wheels to cotton cloth to telephones
and steam engines. In the 20th century, the meaning
of technology was expanded to include satisfying
human material needs and desires, from factories to
scientific knowledge, engineering know-how, and
technological products themselves. One of the most
important technological advances of the 20th century
was computing power. Computers are now involved
in many aspects of technology, but computers are not
all there is to technology.
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
chapter 4
4. Technology is the application of science.
This idea can be traced to the development of
the atomic bomb and radar, both WWII projects
in which scientists (led primarily by physicists)
worked as engineers to create major technologies.
However, it takes more than the application of
science to create a new technology. Technology
requires both science and engineering, but the
goals of science and engineering are different. The
goals of science are to understand why and how
nature works, while engineering aims to shape the
natural world to meet what humans want and need.
5. Technology follows its own course, independent
of human direction.
In other words, the misconception is that
technology affects society, but society does not
affect technology. In reality, technology mirrors
our values, as well as our flaws. Some technological
advances are viewed as undesirable
or objectionable by some people,
and advantageous by others.
Some advances harm the
environment, while others have
advantages for some groups
of people, animals, plants, generations, etc. Some
technologies appear sensible at the time, but decades
or centuries later are found to have undesirable
consequences. It is important to give considerable
thought to advantages and disadvantages before
developing a new technology. We can decide which
technologies should and should not be pursued
(an excellent example is human cloning). Most
importantly, these decisions are up to humans.
3 American
Chemical Society (1998). ChemSource: SourceBook,
v. 2.1, vol 4, THER-p. 38.
4 See
pp. 50-52 of National Academy of Engineering,
National Research Council (2002). Technically Speaking:
Why All Americans Need to Know About Technology.
(Washington, D.C.: National Academy Press)
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chemical dominoes
Investigate
1.
CO2 generation is directly
related to the What Do You
Think? illustration. The
information on the board
and the equipment on the lab
bench is related to Method 1 in
Investigate.
2.
Students will become experts
at one method of generating
CO2, and then will present their
findings to the class. Based on
this, the class will determine
important criteria on which to
judge each method.
3. a-c)
There may be more than one
correct answer, depending on
the criteria selected. Some of
the criteria that may be selected
are: the speed of gas generation,
the cost of materials, the ease
of cleanup, and safety of the
procedure. It is important
that students make careful
observations and measurements,
as instructed.
Important note: Make sure
students record how much
baking soda is needed in
Method 1 to be able to tip the
lever by 2 cm. They will need
this information to use again in
Section 3, Part C, Step 4.
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Method 1
Starting materials: Sodium
bicarbonate and acetic acid
(baking soda and vinegar)
Students will use all of what is
set out for them to practice with,
so only set out a small amount,
perhaps 5 g. The actual amount
of baking soda needed is only a
little more than 0.1 g (0.123 g),
although more will be needed
to inflate the balloon against the
balloon’s resistance to inflation.
Theoretically, only about 2 mL
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
Method 2
chapter 4
Starting materials:
Calcium carbonate and
hydrochloric acid (1.0 M HCl)
Again, students will use all
of what is set out for them to
practice with, so only set out
a small amount, perhaps 5 g.
The actual amount of calcium
carbonate needed is only a
little more than 0.1 g (0.147 g),
although more will be needed to
inflate the balloon against the
balloon’s resistance to inflation.
Theoretically, only about 3 mL
of 1.0 M HCl is needed. You
might want to tell the students
to use 10 mL of the HCl in order
to save time and to ensure that
the calcium carbonate is the
limiting reagent.
of vinegar is needed. You might
want to tell the students to use
5 mL of vinegar in order to save
time and to ensure that the baking
soda is the limiting reagent. The
best procedure for this method
is to place the weighed NaHCO3
in the Erlenmeyer flask, clamp
the flask down, and pour the
vinegar into the balloon. While
the top of the balloon hangs
limply to the side, fix the opening
of the balloon securely over the
mouth of the flask. The reaction
is initiated when the top of the
balloon is lifted, spilling the
vinegar into the flask.
The best procedure for this
method is to place the weighed
CaCO3 in the Erlenmeyer flask,
clamp the flask down, and
pour the HCl into the balloon.
While the top of the balloon
hangs limply to the side, fix the
opening of the balloon securely
over the mouth of the flask. The
reaction is initiated when the top
of the balloon is lifted, spilling
the HCl into the flask.
They should check for increased
Tell the students that they should temperature and the evolution
of a gas. In this method, it is
run at least two trials to be sure
again difficult to tell whether
of their observations.
the system gains or loses energy
as there is little change in
They should check for increased
temperature and the evolution of temperature. However, it is clear
a gas. In this method, it is difficult that disorder increases with the
generation of a gas.
to tell whether the system gains
or loses energy as there is little
change in temperature. However,
it is clear that disorder increases
with the generation of a gas.
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chemical dominoes
Method 3
Starting material:
Calcium carbonate
This method will require rather
strong heating for some time
in order to inflate the balloon.
Theoretically, the same amount
of calcium carbonate will
be required as in Method 2
(0.147 g) but using 2-5 times
as much should speed the rate
of inflation. Students may ask
for a scale because it is difficult
to tell whether a change has
occurred (both CaCO3 and CaO
are white crystals), but they can
prove that something happened
if they measure the mass of the
salt before and after the heating.
Make certain they allow time for
the flask to cool before placing it
on the balance. (You may want
to wait until the need arises
to offer the scale, or you may
simply have it available and let
students figure out what to do
with it.)
In this method, the energy of
the system increases
(endothermic) and disorder
increases (formation of a gas).
Because of the intense heating
required, this may be considered
the least safe method.
Method 4
Starting material:
Carbonated beverage
This can be done as a teacher
demonstration as the Student
Edition suggests, or you can
provide the carbonated beverage
for a few groups to experiment
with. Some figures for the
solubility of CO2 in water
indicate that 700-900 cc of the
624
gas will dissolve in one liter of
water, or about 0.36 M solution.
Gases are more soluble in cold
solvents than in warm solvents.
By heating the carbonated
beverage, CO2 is driven out
and will inflate the balloon.
You (or the students) will place
a freshly opened, partially full
bottle of club soda in very warm
water or drop a hot object into
the liquid and quickly pull a
balloon over the neck of the
container. The CO2 will come
out of solution and fill the
balloon. While any carbonated
beverage will work, one without
sugar or other additives will be
easier to clean up in the event
of a spill. Assuming some losses
and incomplete “degassing”
of the liquid, 100 mL of cold
carbonated beverage should
inflate the balloon.
In this method, heat is added
and so it is an endothermic
process. A gas is generated,
making the disorder increase.
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
chapter 4
Chem Talk
Students learn the specifics
about the energy and entropy
changes involved in the four
CO2 production methods that
they tested. An explanation of
how substances absorb and
release energy through chemical
reactions based on energy stored
in chemical bonds is presented.
Endothermic and exothermic
changes are defined and
explored. Entropy is presented as
the disorder in matter. The focus
is on how entropy changes as
state of matter changes.
A Blackline Master of the
diagrams depicting enthalpy
and entropy is available on the
Teacher Resources CD.
4-1a
4.
6. a-b)
You may want have one member
of each team record data they
have observed on the board
while other members of the
group demonstrate the method
for the class.
Students return to home groups
for this step. Guide the groups to
establish criteria they should use
to make their decision. Criteria
students might suggest are cost,
excitement, speed, output, ease
of operation, safety. Encourage
students to consider safety as one
of the criteria although you may
have to help them to know what
is safer and what is less safe.
5.
Solid materials can be disposed
of in the trash. Liquid materials
can be disposed of in the sink,
rinsing with plenty of water.
Blackline Master
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chemical dominoes
Checking Up
1.
A chemical bond holds atoms
together inside a molecule
when electrons are shared.
Outside a molecule, electrostatic
intermolecular forces can exist
between molecules in close
proximity but these forces are
much weaker than a chemical
bond, often by a factor of 100
or more.
2.
The competition is between the
energy required to break original
bonds (endothermic) and the
energy released when new bonds
are formed (exothermic). If more
energy is released when new
bonds form than it required to
break the original bonds, the
reaction is exothermic.
3.
Entropy
4.
A gas has more disorder than a
solid (or a liquid) because there
is much less restriction in its
ability to move about. Volume is
not constrained in a gas as it is
in a solid (or liquid).
Students’ criteria for
determining the best recipe
What Do You Think Now? may include best taste, fewest
ingredients, least preparation
You may want to take another
time, simplicity, fewest calories,
look at the What Do You See?
least expensive, or others.
illustration at the same time you
reconsider the What Do You
Think? questions. See if students’ The energy of chocolate-chip
cookies is greater than the
conclusions differ from those
ingredients. Students know this
they had before the section
because baking cookies is an
and share with them the answer
provided in A Chemist’s Response endothermic change. You may
point out to students that baked
to reopen a discussion.
cookies have more calories
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– energy – than cookie batter
because baking converts starch
to digestible carbohydrates.
The entropy (disorder) of the
cookies increases because the
ingredients are mixed together
better (more homogeneous)
after baking rather than being
individual ingredients. However,
the baked cookie has particles
more fixed in location than
cookie batter does, indicating a
loss of entropy.
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
Notes
chapter 4
Active Chemistry
629
chemical dominoes
SYMBOLIC —
Start
End
Disorder
More
Less
End
Start
Chem Essential
Questions
What does it mean?
MACRO — Students’ answers
may vary.
Disorder of matter increases – a
solid changes to a liquid, liquid
changes to a gas, substances are
mixed together, etc.
Disorder of matter decreases
– a gas changes to a liquid, a
liquid changes to a solid, mixed
substances are separated.
Energy of matter increases – the
temperature of the matter (in
a system) increases because the
particles are moving faster or the
temperature of the surroundings
decreases because the particles
have absorbed and stored energy
(endothermic).
Energy of matter decreases – the
temperature of the matter (in a
system) decreases because the
particles are moving more slowly or
the temperature of the surroundings
increases because the particles have
released energy (exothermic).
NANO — Students’ answers
may vary.
As disorder of particles increases,
the distance between particles
may increase. Another increase
in disorder occurs when two
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different types of particles are
mixed together, such as when salt
is dissolved in water. As disorder
of particles decreases, the distance
between particles may decrease as
in a change of state.
If two atoms are bonded together
and the bonding electrons absorb
energy, the bond may be broken. If
two unbonded atoms are attracted
to each other and form a bond, the
atoms become more stable (lower
potential energy) so they must
release energy.
SYMBOLIC —
Students may choose diagram B on
the first page of Chem Talk as one
example of a change that releases
energy. Another may be a sketch
of something burning, water vapor
condensing, or a bond forming.
Other examples could also be used.
How do you know?
All four methods involved an
increase in entropy because a gas
was produced from either a liquid,
a solid, or combination of liquid
and solid. Method 1 involved
mixing sodium bicarbonate and
acetic acid. There was no measured
temperature change during the
reaction, so the energy change
cannot be determined. Method 2
involved mixing calcium carbonate
and hydrochloric acid. Again there
was no measured temperature
change during that reaction and
so, energy change cannot be
determined. Method 3 required
heating calcium carbonate which
means the matter gained energy
(it was an endothermic change).
Gas was released into the balloon,
so entropy increased. Method 4
involved heating carbonated water.
Energy was transferred to the
water, so the water experienced
an endothermic change. Entropy
increased with the escaping gas.
Why do you believe?
Students’ answers may vary. One
example might be cooking over
an open fire. As the log burns, it
releases energy in the form of heat.
This heat is absorbed by the air and
the food near the burning log. The
added energy causes the molecules
in the air to move more quickly,
thus becoming more disordered.
The food absorbs the energy as it
cooks. Gases are generated (CO2
and H2O) which means that entropy
is increasing.
Why should you care?
Students’ answers might include
dropping something from one end
of the lever into another container,
tipping another lever, pulling a
string to initiate another event, and
a myriad of other options.
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
chapter 4
Reflecting on the
Section and the
Challenge
Students should read this
section for a specific, direct
connection between the section
and the Chapter Challenge.
While students do not answer
any questions in this section, it
will provide them with valuable
direction in developing their
Chapter Challenge projects.
You may want to provide some
class time for students to read
this paragraph silently or aloud.
Group work is also a possibility.
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631
chemical dominoes
Chem to Go
1.a)
It is not possible to tell because
no information on heat energy is
provided.
1.b)
The change is exothermic
because water molecules have
less energy as a liquid than as a
vapor because they experience
less movement in the liquid state.
Condensation is an exothermic
process.
1.c)
It is not possible to tell because
no information on heat energy is
provided.
2.a)
Disorder increases because a
solid dissolves in water and a gas
is produced.
2.b)
Disorder decreases because
liquid molecules are more
attracted to each other and
are less free to move than gas
molecules.
2.c)
isorder decreases because the
D
oxygen was originally a gas.
When it bonds with the copper,
a solid is formed.
3.a)
4Fe(s) + 3O2(g) → 2Fe2O3(s)
Reactants – Fe(s) and O2(g),
Product – Fe2O3(s)
2KClO3(s) → 2KCl(s) + 3O2(g)
Reactant – KClO3(s),
Products – KCl(s) and O2(g)
3.b)
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4Fe(s) +3O2(g)
→
2Fe2O3(s)
Disorder decreases because a
gas is consumed and a solid is
produced.
2KClO3(s) → 2KCl(s) + 3O2(g)
Disorder increases because a gas
is produced while no gases are
consumed.
4.
c) A
chemical bond is formed
and energy is released.
5.
a) I t is endothermic and entropy
increases.
6.
a) CaCO3(s)
→
CaO(s) + CO2(g)
7.
Preparing for the
Chapter Challenge
a) Students’ answers will vary
among the four methods.
Their reasoning should
include volume of gas
generated, ease of
generation, expense, and
safety considerations.
SEction 1 ENERGY AND ENTROPY: Alternative REACTION PATHWAYS
It uses the same materials as
Method 2 but the heating
process can be quite lengthy.
Also, for that reason, it could
be considered the least safe
(requiring flame or other
intense heat). Method 4 will
be the easiest to clean up but
might be difficult to control
and may develop the least gas
(least pressure).
b) Students’ answers will vary.
Slow inflation would be more
dramatic in some cases if it
is not too slow. Probably,
Method 3 would provide the
slowest inflation, perhaps too
slow. Method 1 is definitely
not the method of choice for
slow inflation.
chapter 4
Method 1 generates CO2
very quickly but it would be
difficult to control the speed of
generation. Lots of gas can be
generated quite easily, cheaply,
and safely. Method 2 is similar
to Method 1 in most respects;
it would be easier to control by
using larger pieces of chalk for a
slower reaction. Method 3 will
likely be the least popular.
Section 1 – QUiz
4-1b
Blackline Master
Section 1 –
QUIZ ANSWERS
❶
a) The drawing should
show the liquid as
unorganized molecules
filling the bottom of
a container. The gas
should be unorganized
and fill the container.
The solid should be
organized and fill the
bottom of the container.
b) D
isorder decreases
because a disorganized
gas becomes part of an
organized solid.
1. Using this equation, answer the following questions.
→ 2HgO(s)
2Hg(l) + O2(g)
a) Draw diagrams to represent how the organization of
molecules changes in the reaction above.
→
+
b) State if disorder increases or decreases during the reaction
and explain your reasoning.
2. For some reactions to occur, you have to add heat.
Other reactions give off heat as they occur. What is heat?
3. Which of these changes produces an increase in entropy?
a) water freezing into ice
b) water vapor condensing into water
c) ice sublimating to water vapor
d) water that decreases in temperature
4. A process that absorbs heat is called:
a) endothermic
b) exothermic
c) entropic
d) enthalpic
❷Heat is a form of energy.
❸ c) ice sublimating to
water vapor
❹ a) endothermic
❺c) liquids, gases
5. Because of the attractive forces between molecules in ____,
energy has to be put in to change them to ____.
a) gases, liquids
b) gases, solids
c) liquids, gases
d) liquids, solids
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